Parliament met for a brief special session on Saturday to announce the vacancy in the presidency following the resignation of Rajapaksa.
Sri Lanka has said it will go ahead with its deal with Bharat Petroleum Corporation Ltd in oil retailing in the island nation despite opposition from the Marxist JVP, or People's Liberation Front, in the coalition government.
Sri Lanka's former president Mahinda Rajapaksa on Tuesday accepted defeat in the parliamentary elections even before the announcement of the final results.
Incumbent Ranil Wickremesinghe is set to take oath as Sri Lanka's new prime minister of a unity government on Tuesday after his United National Party appeared close to a simple majority, with rival Mahinda Rajapaksa admitting defeat in the closely contested parliamentary polls.